Singularity of creep behavior in Ni3Al at stoichiometry

Systematic investigations on both poly- and single crystalline Ni,AI have shown the existence of singularity of creep behavior at stoichiometry as well as the stress anomaly of the octahedral slip at intermediate temperatures and the athermal stress of the cube slip. We revealed that a viscous motion of dislocations on {111} plane governs the creep deformation of Ni,AI at a temperature range higher than the peak temperature, and that the mechanism governing the stress anomaly persisted its effect on the dislocation motion even at such high temperatures. There are large number of studies attempting to give an explanation for the stress anomaly with a basis of the cross-slip model proposed by Kear and Wilsdorf. Then the cross-slipped parts can be expected to move with a dragging mechanism with a diffusion mechanism at the high temperature range. The double-kink type locking parts are composed of a pair of jogs, one of which acts as a vacancy source and the other acts as a vacancy sink. For the climb motion of both of jogs, vacancy migration is required from ones to the others. A simple model including Kear-Wilsdorf type locking mechanism is attempted to unify the singularity in both creep behavior and stress anomaly in terms of a jog-drag motion of dislocation on {111} slip plane. By taking the effect of Al concentration on inter-diffusion coefficient of Ni3Al, both the singularity at stoichiometry and the effect of the deviation from the stoichiometry on creep behavior could be explained semi-quantitatively, and a path to an extended model for the effect of solid-solution on the creep behavior will be also shown in the presentation.